The pyrolysis of thermolysis of tetraethylammonium borohydride, as described in my prior U.S. Pat. No. 4,150,057, Apr. 17, 1979, "Method for Preparation of a Carboranyl Burning Rate Accelerator Precursor", into bis(tetraethylammonium) decahydrodecaborane ([Et.sub.4 N].sub.2 B.sub.10 H.sub.10) is only accomplished in relatively low yields because of the difficulties involved in controlling the thermolysis reaction. As a result, a considerable quantity of bis(tetraethylammonium) dodecahydrododecaborane ([Et.sub.4 N].sub.2 B.sub.12 H.sub.12) is produced instead of the desired product, bis(tetraethylammonium) decahydrodecaborane. Because of the low yield of the desired product, three other processes have been devised which involve the use of different starting materials to produce a common ingredient, diborane, which is subsequently thermolyzed into decaborane. The decaborane is the essential material for the synthesis of n-hexylcarborane and carboranylmethyl propionate.
Advantageous would be a process which would obviate the undesirable features of the three processes. Such a process for the synthesis of carboranes would be particularly attractive if it offered several major advantages over the other three processes; namely, such as, (a) bypassing the flammable and toxic chemical intermediates, namely, diborane and decaborane; (b) being of low cost; (c) producing a higher yield of an intermediate involved in the production of carboranes.
Therefore, an object of this invention is to provide an improved process for the thermolysis of tetraalkylammonium borohydride to bis[tetraalkylammonium] decahydrodecaboranes.
Another object of this invention is to provide an improved process that yields a higher percentage of bis(tetraalkylammonium) decahydrodecaboranes from the thermolysis of tetraalkylammonium borohydride.